This invention relates to a display device which displays desired image information on a display panel comprising a plurality of display pixels which have current drive type optical elements, and more particularly regarding a display device and the method for driving the display device.
In recent years, personal computer and visual equipment monitors with an electronic screen called a Cathode Ray Tube (CRT) are fast becoming obsolete with the emergence of flat panel display devices, such as Liquid Crystal Display (LCD) flat panel monitors, at an astonishing rate. In particular, LCD's are commonplace because they offer some real advantages over other display technologies. They are thinner, lighter and draw much less power than conventional CRT's. LCD's are all around us everyday as they come in all shapes and sizes ranging from large screen televisions to small laptop computers and Personal Digital Assistants (PDA's), and even smaller cellular phones, digital cameras and many other electronic devices.
As the display device (display) of the next generation following in this revolutionary LCD technology, such as organic electroluminescent (EL) devices (hereinafter referred to as organic EL devices), inorganic electroluminescent elements (hereinafter referred to as inorganic EL elements), or Light Emitting Diodes (LEDs) and the like, full-scale application of the self-light type display (display device) comprising a display panel configured with self-light type light emitting elements called active matrix is evolving. Specifically, an active matrix is a type of LCD where each display element (each pixel) includes an active component such as a transistor to maintain its state between scans, and is also known as Thin-Film Transistor or TFT.
In such a self-light generation display, notably, a self-light type display which applies an active matrix drive method as compared with LCD's, the display speed response is fast with an unrestricted viewing angle. Also, higher luminosity, higher contrast, high definition display panels with much lower power consumption and the like are inevitable in the future. Since backlight is not needed in such an LCD display, it has very predominant characteristics that still more thinly shaped and lightweight models are possible.
This particular type of display panel, briefly, is comprises an array of display pixels which contain light emitting elements arranged near each of the intersecting points of the signal lines and in the direction of the scanning lines set in the line writing direction; a scanning driver applies sequentially scanning signals to predetermined timing and sets the display pixels of a specified line in a selection state; and a data driver generates write-in current (drive current) according to the display data which is supplied to each of the display pixels via signal lines and the above-mentioned write-in current is supplied to each of the display pixels. Each of the light emitting elements performs a light generation operation by predetermined luminosity gradation according to the display data, and the desired image information is displayed on the display panel. Afterwards, the configuration of a self-light generation type display will be described.
In the display drive operation of such a display, individual write-in currents are generated which have a current value according to the display data from the data driver to a plurality of display pixels and supplied simultaneously to the display pixels of a specified line selected by the scanning driver. This is in contrast to a current specification type drive method which repeats successively an operation to make each light emitting element emit light by predetermined luminosity gradation for each line of one screen and the display pixels of a specified line selected by a scanning driver. A Pulse Width Modulation (PWM) type drive method and the like which repeats successively for one screen an operation which supplies constant drive current of a constant value from the data driver, individual time width (signal width) according to the display data, and makes each of the light emitting elements emit light by predetermined luminosity gradation is commonly known.
However, there is a problem in the light emitting element type display mentioned above and the fact they do suffer from this drawback will be explained below.
Specifically, the data driver generates the write-in current according to the display data corresponding to each of the display pixels and the above-mentioned write-in current changes according to the display data in a conventional configuration and a conventional drive controlling method, which are supplied to the display pixels via each of the signal lines connected to an output terminal of the data driver. Thus, the current supplied to a circuit arrangement of transistors, latch circuits and the like which are individually formed in the data driver corresponding to each of the signal lines from a predetermined current source will also change. Here, generally a capacitative element (wiring capacity) exists in the signal wiring. Consequently, current supplied from the above-mentioned current source to the data driver, when supplied to the circuit arrangement via the signal wiring for current supply, the operation which alters the current supplied from the current source is equivalent to the charge or discharging of predetermined electric potential in parasitic capacitance which exists in the signal wiring. As a result, when the current supplied via the signal wiring is extremely low, the charge and discharge operation of the signal wiring for current supply takes time, and by the time the electric potential of the signal lines are stabilized, a relatively lengthy period will be required.
On the other hand, the operational period assigned to a current holding operation and the like in each of the signal lines becomes brief and attains high-speed operation essential in the data driver so the number of signal lines increases in proportion to the buildup of the number of display pixels of the display panel.
However, as mentioned above, the charge and discharge operation of the current supply in the signal wiring requires a certain amount of time, particularly; the current value of the write-in current supplied via the signal lines to the display panel in connection with miniaturization of the display panel or high definition (high resolution) and the like becomes low. It has disadvantages in the amount of time required in the charge and discharge operation of the signal wiring increases, rate controlling of the operating speed of data driver due to the rate of the charge and discharge operation has to be performed and achieving favorable image quality becomes difficult.
Additionally, display devices comprising a conventional data driver are configured so the write-in current is generated according to the display data by the data driver and supplied to the display pixels via each signal line. However, because the write-in current is an analog signal which changes according to the light generation state of the light emitting elements, the signal is easily influenced by external noise or signal degradation which produces a decline or change in the light generation luminosity in the light emitting elements. This problem makes it difficult to obtain a stable image display in suitable luminosity gradation.